Relativity is a branch of physics that deals with the behavior of matter and energy in the presence of gravity and the properties of space and time. It is based on the theory of special relativity developed by Albert Einstein in 1905, and the theory of general relativity developed in 1915.
Special relativity deals with the behavior of objects that are moving at constant speeds relative to each other, and shows that time and space are not absolute, but depend on the observer’s frame of reference. General relativity extends this to include the effects of gravity, showing that gravity is not a force, but a curvature of space and time caused by the presence of mass and energy.
Relativity has many practical applications, including in the design and operation of satellite navigation systems and the correction of GPS signals for relativistic effects. It also plays a crucial role in our understanding of the behavior of black holes, the structure of the universe, and the evolution of the cosmos.